The invention relates generally to database and database management system operations. More specifically, the invention relates to updating an offline IMS Fast Path DEDB database.
The IBM Information Management System (IMS) is a joint hierarchical database and information management system. There are three basic forms of IMS databases: (1) Full Function; (2) High Availability Large Databases; and (3) Fast Path. Full function databases can have both primary and secondary indexes, employ a variety of access methods and can store data using Virtual Storage Access Methods (VSAM) or Overflow Sequential Access Methods (OSAM). High Availability Large Databases are an extension of IMS Full Function databases and were introduced to provide better availability, handling of extremely large data volumes and online reorganization to support continuous availability.
Fast Path databases were designed to be continuously online and are optimized for extremely high transaction rates. That is, Fast Path databases are functionally focused on data acquisition or capture rather than query response. Fast Path databases do not support indexes and, for the most part, are implemented using Data Entry Databases (DEDBs). Fast path DEDBs can only be built atop VSAM and are direct-access databases that consist of one or more areas, with each area containing both root segments and dependent segments.
While DEDBs are designed to be continuously available, there are times when one must be taken offline. For example, structural changes in a DEDB's schema can only be made to an offline database. While offline, however, there is currently no mechanism to update a DEDB. Thus, if a DEDB is to be modified it must currently be made unavailable to users. The time required to make structural changes may be large and the concomitant loss of access to the database can pose a heavy financial burden on the database's owner. Thus, it would be beneficial to provide a means to restructure a DEDB database while it is offline.